Production of solid ammonium perphosphate



Patented June 13, 1939 UNITED, STATES PATENT OFFICE PRODUCTION OF SOLID'AMMONIUM PERPHOSPHATE No Drawing. Application July 29, 1936, Serial No.93,254. I In Germany August 1,1935

11 Claims.

This application is, in part, a continuation of my application SerialNo. 29,737, filed July 3, 1935.

This invention is concerned with the preparation of solid ammoniumperphosphate- It is already' known that ammonium phosphate will formaddition compounds with hydrogen peroxide, the hydrogen peroxide beingpresent as hydrogen peroxide of crystallization analogous'to' the waterof, crystallization present in hydrated compounds. Ammonium phosphatecontaining hydrogen peroxide of crystallization has been frequently butinappropriately termed ammonium perphosphate by chemists, Thisapplication is concerned with the preparation of true solid ammoniumperphosphate, as distinguished from those compounds merely containinghydrogen peroxide of crystallization and erroneously termedperphosphates.

The compounds prepared in accordance with this invention are genuineperphosphates and contain a peroxide group. i. e., an oxygen to oxygenbridge, in the molecule. Up until the present time true ammoniumperphosphate existed only in solution and had not been separated in theform of the solid compound. While ammonium perphosphate has beenpreviously prepared in solution by chemists such as Fichter andGutzwiller, whose work is described in the Helvetica Chimica Acta, Vol.XI, page 333, all previous experiments to obtain this salt in the solidform have been unsuccessful.

Fichter and Gutzwiller prepared ammonium perphosphate in solution by'theelectrolysis of solutions of ammonium phosphate containing fluorides.These experimenters attributed the failure of their attempts to obtainthe salt in the solid form of an inner weakness of the ammoniumperphosphate molecule. In attempting to isolate the solid ammoniumperphosphate salt they believed that the ammonium ion, or thehydrolytically evolved ammonium radical, was oxidized by theperphosphate ion, thus resulting; in decomposition of the compound. Theexperiments of Fichter and Gutzwiller indicate. that the higher theconcentration of ammonium perphosphate in solution the more rapid doesthe decomposition occur. I I have now discovered that it is possible toobtain true ammonium perphosphate in solid form by a very simple methodwhereby the salt is obtained in stable form. In accordance with. myprocess a solution of potassium perphosphate, which maybe easilyprepared electrolytically, is

caused to react under suitable. conditionswitlr an ammonium salt of anacid radical whose potassium salt is less soluble in water than'theammonium salt and the potassium perphosphate. In this way the potassiumsalt resulting from the reaction between the potassium perphosphate andammonium salt is readily removed from the ammonium perphosphate solutionremaining, eitherby concentrating the solution and/or by cooling, ifnecessary. I Amongthe ammonium salts of acids Whose potassium salts areless soluble in waterthan the. corresponding ammonium compound and aretherefore usable in myprocess, I, have found ammonium perchlorate,ammonium persulphate, ammonium nitrate, and ammonium sulphateparticularly suitable. During the double decomposition wherein ammoniumperphosphate is formed, the potassium salt of the acid radical selected,perchlorate, persulphate, nitrate, or sulphate, is precipitated, and theammonium perphosphate remains in solution and may be readily separatedfrom the potassium salt by filtration.

p After removal of the precipitated potassium salt ammonium perphosphatein solid form may be recovered from the solution by various methods. Forexample, it is possible to secure the solid salt by careful evaporationof the solution, e. g, by evaporation under reduced pressure atmoderately high temperatures. We have found a temperature of about C.suitable when the evaporation is carried out in vacuo. In this way it ispossible to obtain true solid ammonium perphosphate in yields as high as97% based on the active oxygen content of the solution.

I may also recover solid ammonium perphosphate from solutions of thatsalt by the addition to said solutions of an organic fluid miscible withwater such as methyl alcohol. This results in the precipitation ofammonium perphosphate in the solid state. The quantity of methyl alcoholto be added corresponds approximately to the quantity of salt solutionto be treated. Theproduct crystallizes out in the form of ammoniumperphosphate containing Water of crystallization and may be readilydried in. accordance with usual methods.

Another method for recovering solid ammonium perphosphate from itssolutions involves the addition to said solutions of an excess ofammonia. This may be readily accomplished by introducing ammonia gasinto the solution to be treated at a relatively low temperature such asone, of 0 C. or below. When saturation of. the solution with ammonia gashas occurred the ammonium perphosphate separates out in the solid statein good yields.

Under some circumstances when precipitating out the ammoniumperphosphate by the addition of ammonia gas to its solution it is notnecessary first to remove the potassium salt in accordance with theprocedure hereinbefore described. If the potassium salt is readilysoluble in an ammoniacal solution the ammonium perphosphate will beprecipitated from the solution leaving the potassium salt behind insolution.

If the solution of ammonium perphosphate, which still contains thepotassium salt, is carefully treated with ammonia practically the totalcontent of ammonium perphosphate can be precipitated out without anydanger of precipitation of the potassium salt.

When taking advantage of the relative insolubility of ammoniumperphosphate in ammoniacal solution, as indicated in the precedingparagraph, it is possible to utilize in the double decompositionreaction between the electrolytically formed potassium perphosphate andthe ammonium salt, an ammonium salt whose corresponding potassium saltis only so slightly less soluble in water than the ammonium salt and thepotassium perphosphate that no precipitation takes place during thereaction. If such potassium. salt is relatively soluble in an ammoniacalsolution it is not necessary that it be first precipitated during thedouble decomposition. When recovering solid ammonium perphosphate inthis way it is desirable to introduce ammonia after the doubledecomposition between the potassium perphosphate and ammonium salt hasoccurred. The ammonium perphosphate is thereby precipitated and thepotassium salt remains behind in solution.

When recovering ammonium perphosphate in this way it is also desirableto have present during the double decomposition an excess of theammonium salt. Ammonium chloride is especially suitable for thispurpose. Ammonium perphosphate, formed by the addition of ammoniumchloride, is readily precipitated by the addition of ammonia as neitherammonium chloride, nor potassium chloride formed as a result of thedouble decomposition, is precipitated from the aqueous solution exceptby a very high concentration of ammonia.

If desired, the separation process utilizing ammonia to precipitate outthe ammonium perphosphate in solid form may also be carried out when thepotassium salts formed during the double decomposition resulting in theammonium perphosphate are either completely or partially precipitatedout during that double decomposition. Before introduction of the ammoniato precipitate ammonium perphosphate the precipitated or partiallyprecipitated potassium salt should be removed.

As examples of my novel process for preparing solid ammoniumperphosphate the following may be given:

Emample I A solution of 500 grams of 95% potassium perphosphate in 900cc. of hot water was prepared. To this. solution a warm saturatedsolution containing 650 grams of ammonium per- The precipitatedpotassium perchlorate was then filtered off using a suction filter. Thesalt was washed in order to free it from traces of ammoniumperphosphate. The filtrate was then precipitated by the addition ofabout 2 liters of methyl alcohol thereto. During the addition of themethyl alcohol the temperature of the ammonium perphosphate solution wasmaintained as low as possible.

The resulting solid salt was 82% ammonium perphosphate (NHi)4P2Oe.2H2O.The yield was 400 grams which corresponds to 91% of the theoretical. Theproduct was filtered under suction and dried.

Example II A solution of 500 grams of 95% potassium perphosphate in 700cc. of hot water was prepared. A solution of 450 grams of ammoniumnitrate in 300 cc. of warm water was also prepared. Before addition ofthe ammonium nitrate to the solution of potassium perphosphate, asdescribed in the next paragraph, that solution was permitted to cool.

The ammonium nitrate solution was then added to the cold potassiumperphosphate solution, the solutions being cooled during the mixing.Upon cooling to 0 C. about 400 grams of potassium nitrate wasprecipitated. This precipitate was removed by filtration and washed tofree it of adhering ammonium perphosphate.

The filtrate, containing ammonium perphosphate in solution, was nextdiluted with about 2.5 liters of water. Ammonia gas was then introduced,the solution being cooled, until the greater part of the ammoniumperphosphate present had been precipitated. In order to determine whenfiltration was complete a filtered sample was periodically titrated. Theprecipitated ammonium perphosphate was then removed by means of asuction filter, the temperature being maintained at about 2 C. The yieldwas 380 grams of 82% ammonium perphosphate and amounted to 87% of thetheoretical.

Example III A solution of 500 grams of 95% potassium perphosphate in 900cc. of water was prepared. To this solution was added a solution of 650grams of ammonium chloride in 1.8 liters of water. During mixing thesolutions were cooled.

A 30% solution of ammonia in water was then added slowly to theresulting clear solution. The mixture was then cooled to -5 C. and theseparated ammonium perphosphate removed by filtration under reducedpressure. The yield was grams of 83% ammonium perphosphate correspondingto 83% of the theoretical.

It should be understood that the various details and amountshereinbefore specified as illustrative are not to be construed asrestricting the invention. The scope of my invention is to be determinedin accordance with the appended claims.

I claim:

1. A process for preparing solid ammonium perphosphate which comprisesthe steps of reacting an aqueous solution of potassium perphosphate withan ammonium salt of an acid radical whose corresponding potassium saltis so much less soluble than said ammonium salt and potassiumperphosphate that the former potassium salt precipitates insubstantially quantitative amounts during the reaction, the conditionsof said reaction, as to concentrations of the aqueous nium perphosphatein order to recover said perreagents and temperature employed during thereaction, being so selected as to insure substantially quantitativeprecipitation of said potassium salt, separating said precipitatedpotassiumsalt and then treating the resulting solution of ammoniumperphosphate to recover said perphosphate in solid form.

2. A process for preparing solid ammonium perphosphate which comprisesthe steps of reacting an aqueous solution of potassium perphosphatewithan ammonium salt of an acid radical whose corresponding potassiumsalt is so much less soluble than said ammonium salt and potassiumperphosphate that the former potassium salt precipitates insubstantially quantitative amounts during the reaction, the conditionsof said reaction, as to concentrations of the aqueous reagents andtemperature employed during the reaction, being so selected as to insuresubstantially quantitative precipitation of said potassium salt,separating said precipitated potassium salt and then evaporating theresulting solution to dryness under reduced pressure in order to recoversaid ammonium perphosphate in solid form.

3. A process for preparing solid ammonium perphosphate which comprisesthe steps of reacting an aqueous solution of potassium perphosphate withan ammonium salt of an acid radical whose corresponding potassium saltis so much less soluble than said ammonium salt and potassiumperphosphate that the former potassium salt precipitates insubstantially quantitative amounts during the reaction, the conditionsof said reaction, as to concentrations of the aqueous reagents andtemperature employed during the reaction, being so selected as to insuresubstantially quantitative precipitation of said potassium salt,separating said precipitated potassium salt and then adding methylalcohol to the resulting solution of ammonium perphosphate in order toprecipitate said salt in substantially solid form therein.

4. A process for preparing solid ammonium perphosphate which comprisesthe steps of reacting an aqueous solution of potassium perphosphate withan ammonium salt of an acid radical whose corresponding potassium saltis so much less soluble than said ammonium salt and potassiumperphosphate that the former potassium salt precipitates insubstantially quantitative amounts during the reaction, the conditionsof said reaction, as to concentrations of the aqueous reagents andtemperature employed during the reaction, being so selected as to insuresubstantially quantitative precipitation of said potassium salt,separating said precipitated potassium salt and then introducing ammoniainto the resulting solution of ammonium perphosphate in order toprecipitate said ammonium perphosphate in solid form.

5. A process for preparing solid ammonium perphosphate which comprisesthe steps of reacting an aqueous solution of potassium perphosphate withan ammonium salt selected from the group which consists of ammoniumperchlorate, ammonium persulphate, ammonium nitrate and ammoniumsulphate, the conditions of said reaction as to the concentrations ofthe aqueous reagents and the temperature of the reaction mixture beingso selected as to, insure substantial precipitation of a potassium salthaving an anion similar to that of said ammonium salt utilized,separating the precipitated potassium salt, and then treating theresulting solution of ammophosphate in solid form.

6. A process for preparing solid ammonium perphosphate which comprisesthe steps of reacting an aqueous solution of potassium perphosphate withammonium perchlorate, the conditions of said reaction as to theconcentrations of the aqueous reagents and the temperature of thereaction mixture being so selected as to insure substantialprecipitation of potassium perchlorate, separating the precipitatedpotassium perchlorate, and then treating said resulting solution ofammonium perphosphate in order to recover said perphosphate in solidform.

7. A process for preparing solid ammonium perphosphate which comprisesthe steps of reacting an aqueous solution of potassium perphosphate withammonium sulphate, the conditions of said reaction as to theconcentrations of the aqueous reagents and the temperature of thereaction mixture being so selected as to insure substantialprecipitation of potassium sulphate, separating the precipitatedpotassium sulphate, and then treating the resulting solution of ammoniumperphosphate in order to recover perphosphate in solid form.

8. A process for preparing solid ammonium perphosphate which comprisesthe steps of reacting an aqueous solution of potassium perphosphate withan ammonium salt of an acid radical Whose corresponding potassium saltis readily soluble in aqueous ammonia solutions and but slightly lesssoluble in aqueous solutions than the ammonium salt and potassium salt,the conditions of said reaction as to the concentrations of the aqueousreagents and the temperature of the reaction mixture being so selectedas to insure substantial precipitation of said potassium salt, removingthe partially precipitated potassium salt and introducing ammonia intothe resulting ammonium perphosphate solution in order to precipitatesolid ammonium perphosphate therein.

9. A process for preparing ammonium perphosphate in solid form whichcomprises reacting an aqueous solution of potassium perphosphate with anammonium salt of an acid radical whose corresponding potassium salt isso much less. soluble than said ammonium salt and potassium perphosphatethat the former potassium salt precipitates in substantiallyquantitative amounts during the reaction, the quantity of water presentbeing so restricted as to insure substantially quantitativeprecipitation at the temperature selected for the reaction, maintainingthe temperature of the reaction below about C., separating saidquantitatively precipitated potassium salt, and then treating theresulting solution of ammonium perphosphate to recover said perphosphatein the solid form.

10. A process for preparing ammonium perphosphate in solid form whichcomprises reacting an aqueous solution of potassium perphosphate with anammonium salt of an acid radical whose corresponding potassium salt isso much less soluble than said ammonium salt and potassium perphosphatethat the form potassium salt precipitates in substantially quantitativeamounts during the reaction, the quantity of water present during saidreaction being so restricted as to insure substantially quantitativeprecipitation at the temperature selected for said reaction, maintainingthe temperature during said reaction below about 0 C., separating saidquantitatively precipitated potassium salt, and then introducing ammoniainto the resulting solution of ammonium perphosphate in order toprecipitate said ammonium perphosphate therefrom in the solid form.

11. A process for preparing solid ammonium perphosphate which comprisesthe steps of reacting an aqueous solution of potassium perphosphate withan ammonium salt of an acid radical whose corresponding potassium saltis readily soluble in aqueous ammonia solutions and but slightly lesssoluble in aqueous solutions than the

